It’s on preview:

EggZavier is allegedly the undead beastmaster, whose loot table contains every egg in the game, up to and including Mythic rarity*. This year he will also drop a selection of HEROIC Eggs... find him and kill him for a chance to get the egg you always dreamed of!

* Arcanes are excluded to preserve rarity

Eggzavier only hangs out for 30 seconds, so catch him while you can!